Rapidly rechargeable battery

ABSTRACT

Design of a rapidly rechargeable gas battery is disclosed. In one embodiment, a rapidly rechargeable gas battery is constructed of a plurality of high surface area, gas adsorbing electrodes and an electrolyte, wherein, during charging operation, gases are formed and adsorbed at the plurality of electrodes such that they generate an electrochemical potential for discharge of the cell formed by electrodes and electrolyte until the state-of-charge has become negligible (deep discharge). The rapidly rechargeable gas battery is designed such that it can withstand high charging current and a deep discharge without irreversible changes in the electrode materials.

FIELD

The following disclosure generally relates to devices forelectrochemical energy generation (e.g., fuel cells and batteries), andmore specifically to rapidly rechargeable gas batteries that aretolerant to fast charging and deep discharging.

BACKGROUND

Any battery consists of two electrodes, an anode and a cathode, and someform of electrolyte. The electrodes are typically made ofelectrochemically active materials. Electrolytes can be liquid, gel, orother materials capable of conducting electric current. Once theelectrodes are immersed into the electrolyte, electrochemical reactionstake place and current will flow upon connecting an external loadbetween the electrodes.

Gas bubbles evolving from electrodes in batteries may be observed duringcharging and discharging. The phenomenon has been observed in lead-acidand Ni/Cd batteries for example. This gas evolution does not contributeto the intended energy storage and power generation by the battery. Infact, it may be detrimental to the proper functioning of the batterywhere the voltage should be determined only by the chemical energy ofthe reactants stored in the electrode materials. However, gases alsohave electrochemical potential. This fact may be used for making abattery in which immobilized gases stored in or at the electrodes arethe working materials (reactants). Such a battery is called a gasbattery, while a similar device that uses flowing gases as reactants iscalled a fuel cell.

The concept of a gas battery operating on immobilized gases as reactantsduring discharge was demonstrated by Sir William Grove in 1839. The samewell-known experiment led later to development of the fuel cell which isfed by flowing gases as reactants. Grove's gas battery consisted of twoplatinum spiral electrodes immersed in sulfuric acid electrolyte. Duringbattery charging, hydrogen was adsorbed on one electrode and oxygen onanother. Grove's experiments laid the conceptual basis for thedevelopment of both the gas battery and the fuel cell. Thus far, onlythe fuel cell has become well-known as a potential highly efficientcontinuous power generator. The combination of materials used by Grovein his experiment was not suitable for development of a gas battery,that is, an energy generator based on storing gases as reactants,although the device he operated clearly demonstrated the concept of ahighly efficient pulse-power generator. While some activity related todevelopment of gas batteries was reported in the 1950-1960s, it neverled to a commercial device because of inherent limitations of theelectrode materials available at that time.

SUMMARY

At least one embodiment of this disclosure pertains to a rapidlyrechargeable gas battery.

In one embodiment, a rapidly rechargeable gas battery is constructed ofa plurality of high surface area, gas adsorbing electrodes and anelectrolyte, wherein, during charging, gases are formed and adsorbed atthe plurality of electrodes creating an electrochemical potential. Therapidly rechargeable gas battery is designed to withstand high chargingcurrent and a deep discharge without irreversible changes in theelectrode materials.

In another embodiment the high surface area, gas adsorbing electrodesare made of different materials to increase the adsorption of gases.Further, the electrodes may be of similar or differing geometry toimprove gas adsorption.

In yet another embodiment separate anode and cathode compartments may becreated by inserting a membrane between the electrodes. These separatecompartments allow for a different electrolyte to be used by eachelectrode to increase adsorption and thereby increase battery capacity.

A permselective membrane may be disposed on the electrodes to preventworking gases adsorbed on the electrodes to be spontaneously desorbedinto the electrolyte resulting in self discharge of the battery.

The electrolyte used in various embodiments of the disclosure can beselected to maximize adsorption at the electrodes. The electrolyte canbe organic or inorganic in nature and the ions which carry the electriccurrent can be simple or complex.

These and other objects, features and characteristics of the presentinvention will become more apparent to those skilled in the art from astudy of the following detailed description in conjunction with theappended claims and drawings, all of which form this specification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of a gas battery that is constructed accordingto the technique described herein.

FIG. 2 shows an example of a multi cell battery composed of gas batterycells.

FIG. 3 shows a graph depicting a charge and discharge cycle of anexemplary gas battery constructed according to the technique describedherein.

FIG. 4 shows a graph of experimental results of battery endurance during1,000 charge/discharge cycles of an exemplary gas battery constructedaccording to the technique described herein.

FIG. 5 shows a graph of the data in FIG. 4 on second order regressionand a battery cycle lifetime calculated from the data.

FIG. 6 is a table of potential gases and the various boilingtemperatures and absorption rates associated with them.

FIG. 7 shows a chart of experimental results on the impact of workinggas selection on battery capacity.

FIG. 8 shows a graph of measured self discharge rate and cumulative selfdischarge of an exemplary gas battery constructed according thetechnique described herein.

DETAILED DESCRIPTION

Those of skill in the art will appreciate that the invention may beembodied in other forms and manners not shown below. It is understoodthat the use of relational terms, if any, such as first, second, top andbottom, and the like are used solely for distinguishing one entity oraction from another, without necessarily requiring or implying any suchactual relationship or order between such entities or actions.

Although the concept of a gas battery is well established historically,the concept of an advanced, high-performance gas battery as claimed inthis patent is made possible only by recent advances such as thecreation of nano-materials. A practical format for storing in-situdeveloped gas in commercially competitive devices is provided only bymaterials with extremely high interfacial area such as nano-materials.Many of these materials also are characterized by excellentelectrochemical reversibility when used as substrates for gas productionand consumption. Gas batteries with these combined characteristics ofhigh energy density and excellent catalytic reactivity can play a veryimportant role in electric vehicle technology. For example, the chargingtime of gas batteries will be orders of magnitude shorter than that ofsolid-state based advanced batteries including lithium ion and nickelmetal hydride batteries. Gas batteries also may be deep-cycled unlikemost existing advanced batteries.

The major advantages of a gas battery, particularly for automotiveapplications, are tolerance to fast charging and deep discharging,simplicity, low cost, light weight, and long shelf life. Mostimportantly a gas battery according to this disclosure can endure a highcharging current. This means drastically reduced charging times.Similarly, a gas battery can sustain high discharge currents and deepdischarging. Other batteries subjected to these conditions would sufferirreversible changes in electrode materials.

In one embodiment, a gas battery operates using reversible oxidation andreduction reactions. During battery charging, electrolysis of theelectrolyte takes place at the electrodes, which produces gases. Thesegases may be adsorbed on the electrodes if the electrodes are made ofadsorbing material. One example of an adsorbing material is activatedcarbon. A reverse process takes place during battery discharge.

FIG. 1 shows an example of a gas battery that is constructed accordingto the techniques described herein. While specific materials andsolutions are mentioned in the description of FIG. 1 it will be apparentto one of skill in the art that other materials and solutions may besubstituted and this description is in no way limiting. It will furtherbe apparent that not all embodiments falling within the scope of thisdisclosure are specifically described.

The example of FIG. 1 includes electrodes 2 and 4 which can be either ananode or a cathode. The electrodes are preferably made from an adsorbingmaterial such as, but not limited to, activated carbon. Tunablenano-porous carbon, or another high surface area adsorbent created usingnano-technology or other technology can be used to increase theadsorption of the gases created during charging. Advances innano-materials have led to materials with specific surface area muchgreater than 500 m²/g. The electrodes may be made of the same ordifferent adsorbing materials to maximize adsorption capability therebyincreasing battery capacity.

Similarly, the electrodes may be of the same or different geometry.Different geometries can be used to attain greater adsorption of theworking gas at the electrode. Further, various geometries andconfigurations can be used to maximize charging current without bubbleevolution. Examples of electrode geometry include cylindrical, planar,and spherical electrodes; examples of configurations are concentric andparallel electrodes.

The electrodes 2 and 4 are housed in a gas tight vessel 8. The vessel issealed with gas tight fittings 10. As will be appreciated, any suitablecomposition and structure for the vessel and gas tight fittings may beused. For, example, plastic would be suitable.

In one embodiment the gas tight vessel 8 is filled with a liquidelectrolyte 6 surrounding the electrodes 2 and 4. This electrolyte canbe any solution of chemical compounds which form positive and negativeions. The ions may be simple or complex. Additives may be introducedinto the electrolytes to improve performance. An example of electrolyteis a solution of NaCl in water. Working gases is this case could behydrogen and chlorine.

This combination of highly adsorbing electrodes and reversible reactionsthat generate and decompose adsorbed gases at the electrodes are keyrequirements for practicality of a gas battery. Another key requirementis to provide enough ionic capacity in the form of electrolyte toachieve practically interesting levels. However, a large cell volumebetween the electrodes would result in poor power density. In principle,a compromise can be achieved by optimizing the shape and configurationof the electrodes. Alternatively, a cell with flowing electrolyte (flowbattery) can be used, however, the well-known drawbacks of flow-typebatteries are various engineering, materials, and cost issues that maybe hard to overcome.

In another embodiment, the vessel can be divided by optional membrane 18to create separate electrolyte compartments for the electrodes 2 and 4.The membrane can be of any suitable construction. However, ideally themembrane should be impermeable to the liquid electrolyte 6. The creationof separate electrolyte compartments for the anode and the cathode ofthe gas battery allows for use of electrolytes having different chemicalcompositions in each compartment. Having different electrolytes in theanode and cathode compartments can maximize adsorption, and therebybattery capacity, by selecting ideal working gases for each electrode.

In yet another embodiment, optional permselective membrane 16 can bedisposed around the electrodes to prevent the adsorbed working gasesfrom being spontaneously desorbed back into the electrolyte resulting inself discharge. The working gases considered to be effective for use ina high capacity gas battery are highly soluble in the electrolyte. Forexample, a gas battery constructed according to the example provided inthis disclosure with a solution of NaCl and water as electrolyte wasfound to have a self discharge rate approximately ten times higher thana commercial NiMH battery.

The permselective membrane 16 can be selected to be substantiallyimpermeable to the working gas created in electrolyte 6. Further, if adifferent electrolyte is used in the anode and cathode compartments thepermselective membrane surrounding each of the electrodes can be ofdifferent materials to optimize performance with the working gases foundin each compartment.

Electrically conductive components 12 and 14 are electrically connectedto the electrodes 2 and 4 and enable redox reactions at the electrodes.Any suitable conductive material, such as graphite, can be used toconstruct these electrically conductive components.

A simple, non-limiting, example of FIG. 1 in operation is describedbelow. The electrolyte for this example includes a simple water solutionof table salt and the electrodes include activated carbon, preferablywith a high surface area. In practice the electrolyte may be anysolution which contains positive and negative ions. Similarly, theelectrodes may be of any composition or geometry as apparent to oneskilled in the art.

One advantage of the batteries according to this invention is the longshelf life. Prior to operation this battery may be stored in one ofseveral states including dry, charged, and discharged. If the battery isstored dry, the electrolyte must be introduced prior to usage.

A current applied across the electrodes 2 and 4, through the graphiterods 12 and 14, charges the battery. During charging, the H⁺ and Cl⁻ions in simple electrolyte 6 of this example will be consumed to formhydrogen gas and chlorine gas at the electrodes.

2NaCl+2H₂O

H₂+2NaOH+Cl₂

The hydrogen gas created during this charging cycle will be adsorbed onone electrode 2 and the chlorine gas will be adsorbed on the otherelectrode 4.

When a load, for example the electric motor of an automobile, isconnected across the electrodes 2 and 4 through the graphite rods 12 and14, the battery is discharged. During discharge, or a load cycle, thegases will be desorbed from the electrodes and the reaction describedabove, with regard to the charge cycle, will proceed in the reversedirection.

H₂+2NaOH+Cl₂

2NaCl+2H₂O

FIG. 2 shows an example of a multi-cell battery 20 composed of multiplegas battery cells. In one embodiment the individual cells of the batteryshown in FIG. 2 can be constructed similarly to the battery describedabove in reference to FIG. 1. Further, the individual battery cells inFIG. 2 may be configured in series, parallel, or a combination of thetwo in order to deliver the desired voltage and current.

In the example of FIG. 2 the cells 24 a-24 n and 26 a-26 n of themulti-cell battery are contained in an outer enclosure 22 which may beof various constructions. The terminals of the various cells in theexample of FIG. 2 are connected in a series/parallel combination. Theconnecting elements 28 may be of any conductive material that issuitable for the application. The connecting elements connect theterminals of the various battery cells to external terminals 30 and 32on the outer enclosure to provide for the load or charger to beconnected. In other embodiments the multi-cell battery may contain cellbalancing electronics to improve performance and battery life.

FIG. 3 shows a graph depicting a charge and discharge cycle of a gasbattery constructed according to the example above with a simple NaClelectrolyte solution. Operation of the battery in the charging modeshows its ability for quick charge with minimal polarization.

During discharge an almost ideal Nernstian behavior is observed overlong discharge times suggesting the potential for high energy density.Further, the battery according to this invention allows for deepdischarging without damage to the electrodes.

A gas battery constructed according to this disclosure, having anelectrolyte solution of water and NaCl and activated carbon electrodes,was further tested for endurance over a series of charge-dischargecycles. The endurance testing was automated with a battery analyzer andcharger controlled by a computer. Prior to the endurance test thecapacity of the battery was experimentally estimated as 0.5 mA-h.

FIG. 4 shows the data from the endurance test comprised of 1,000charge-discharge cycles. The charge current was set at 25 mA orapproximately 50 c. Charging was stopped when the battery capacity of0.5 mA-h was reached. The battery was then discharged at a current of 25mA or approximately 50 c. Discharging was stopped when the batteryvoltage dropped below 0.3 V. The battery voltage at the beginning ofeach discharge cycle was 1.5-2 V. Discharge capacity was calculated foreach charge-discharge cycle and round trip efficiency was estimated foreach cycle as discharge capacity over charge capacity.

FIG. 5 shows the experimental data of FIG. 4 approximated with a secondorder regression. The battery cycle life was calculated from thedischarge capacity as a percentage of the initial discharge capacity.The battery lifetime was estimated as the number of charge/dischargecycles when the discharge capacity dropped below 80% of its initialvalue. From the estimated data of FIG. 5 the cycle life of the testbattery was approximately 400 cycles.

FIG. 6 is a table showing the adsorption of various gases by one gram ofactivated carbon at 15° C. Different electrolytes produce differentgases. These working gases are adsorbed and desorbed at differentcapacities by different materials. For example the adsorption of carbondioxide (CO₂) by activated carbon is an order of magnitude higher thanadsorption of hydrogen (H₂). Selection of working gases is important inorder to increase the specific energy density of gas batteries.

Data on adsorption of various gases by activated carbon suggest thatgases with a higher boiling point may be more attractive candidates.Examples of candidate working gases are, but are not limited to, SO₂,Cl₂, NH₃, H₂₅, CO₂, O₂, H₂. Preferably the electrodes have an adsorptioncapacity of the working gas as high as possible. The adsorption capacityof the working gas on the electrodes is preferably greater than 50cm³/g.

The effect of working gas selection on battery capacity wasexperimentally tested. A second example battery, using Cl₂ and NH₃ asworking gases instead of Cl₂ and H₂, was constructed. This wasaccomplished by using a saturated solution of NH₄Cl in water aselectrolyte. The measured capacity of the example Cl₂/NH₃ battery wasobserved to be 5.5 times higher than for the Cl₂/H₂ battery. Thisincrease in capacity is shown in FIG. 7. The observed increase incapacity demonstrates importance of selection of working gases tomaximize battery capacity.

In addition to using a single electrolyte compartment, anode and cathodecompartments separated by a membrane may be used as described withreference to an embodiment of FIG. 1. The chemical composition of theelectrolyte in the anode and cathode compartments may be different. Inthe case where different electrolytes are used in the anode and cathodecompartments the membrane should be impermeable to the liquidscomprising the electrolytes.

Another important parameter of any battery is self discharge rate. Theexample gas battery of FIG. 1 with a NaCl electrolyte was tested forself discharge by keeping the fully charged battery at open circuit andmeasuring self discharge current and voltage decline. Self dischargetests were performed by charging the battery with a 25 mA current untilthe capacity of 0.5 mA-h was reached. Discharge current and open circuitvoltage were then monitored until the battery voltage dropped below 1 V.Experimental results are shown in FIG. 8. A commercial NiMH battery wastested for self discharge under the same conditions. The measured selfdischarge of gas battery was found to be 9.8 times higher than themeasured self discharge of the commercial NiMH battery. Self dischargerate may be reduced by selection of active ingredients of theelectrolyte.

The operation of a gas battery with complex chemistry, such as Cl₂/NH₃battery, for example, will require special measures to be taken againsthigh self discharge. One option to reduce self discharge is toincorporate a permselective membrane surrounding the electrode. Such amembrane should be impermeable to gases formed during electrolysis.

Operation of the battery at pressures above atmospheric and temperaturesbelow or above room temperature may also improve performance bymaximizing adsorption during charging and minimizing desorption in a noload state (self discharge).

The description and drawings provided herein show exemplary embodimentsof the invention. It will be appreciated to those skilled in the artthat the preceding examples and embodiments are exemplary and notlimiting to the scope of the present invention. It is intended that allpermutations, enhancements, equivalents, combinations, and improvementsthereto that are apparent to those skilled in the art upon a reading ofthe specification and a study of the drawings are included within thetrue spirit and scope of the present invention. It is therefore intendedthat the following appended claims include all such modifications,permutations and equivalents as fall within the true spirit and scope ofthe present invention.

1. A rapidly rechargeable battery utilizing chemical energy of gasescomprising: an electrolyte; and a plurality of gas adsorbing electrodesimmersed in the electrolyte, each electrode having a specific surfacearea greater than 500 m²/g, wherein during charging, gases are adsorbedon the plurality of electrodes.
 2. The rapidly rechargeable battery ofclaim 1 further comprising a permselective membrane disposed around eachelectrode, wherein the permselective membrane is substantiallyimpermeable to the gases adsorbed on the electrodes.
 3. The rapidlyrechargeable battery of claim 1 further comprising separate electrodecompartments for each electrode.
 4. The rapidly rechargeable battery ofclaim 3 wherein the electrolyte in each electrode compartment has adifferent chemical composition.
 5. The rapidly rechargeable battery ofclaim 1 wherein the electrolyte includes a solution of chemicalcompounds which form positive and negative ions.
 6. The rapidlyrechargeable battery of claim 5 wherein the ions include simple ions. 7.The rapidly rechargeable battery of claim 5 wherein the ions includecomplex ions.
 8. The rapidly rechargeable battery of claim 5 wherein theions form gases on the plurality of electrodes via electrolysis processduring charging.
 9. The rapidly rechargeable battery of claim 1 whereineach of the plurality of electrodes includes an electrically conductivecomponent to enable redox reactions at the plurality of electrodes. 10.The rapidly rechargeable battery of claim 9 wherein the electricallyconductive component includes graphite.
 11. The rapidly rechargeablebattery of claim 1 wherein the plurality of electrodes include the samematerial.
 12. The rapidly rechargeable battery of claim 1 wherein theplurality of electrodes each include different materials.
 13. Therapidly rechargeable battery of claim 1 wherein the plurality ofelectrodes have a cylindrical geometry.
 14. The rapidly rechargeablebattery of claim 1 wherein the plurality of electrodes have a planargeometry.
 15. The rapidly rechargeable battery of claim 1 wherein theplurality of electrodes have a spherical geometry.
 16. The rapidlyrechargeable battery of claim 1 wherein the plurality of electrodes havea parallel configuration.
 17. The rapidly rechargeable battery of claim1 wherein the plurality of electrodes have a concentric configuration.18. The rapidly rechargeable battery of claim 1 wherein the plurality ofelectrodes have varied geometries.
 19. The rapidly rechargeable batteryof claim 1 wherein the plurality of electrodes are constructed ofmaterials including activated carbon.
 20. The rapidly rechargeablebattery of claim 1 wherein the plurality of electrodes are constructedof materials including tunable nanoporous carbon.
 21. The rapidlyrechargeable battery of claim 1 wherein the plurality of electrodes areconstructed of materials including gas adsorbing nano-materials.
 22. Therapidly rechargeable battery of claim 1 wherein the gases formed duringcharging are selected to be effectively adsorbed on the plurality ofelectrodes and desorbed from the plurality of electrodes duringdischarging.
 23. The rapidly rechargeable battery of claim 20 whereinthe gases formed are selected from the group consisting of: SO₂, Cl₂,NH₃, H₂S, CO₂, O₂, and H₂.
 24. The rapidly rechargeable battery of claim1 wherein the electrolyte includes organic components.
 25. The rapidlyrechargeable battery of claim 1 wherein the electrolyte includesinorganic components.
 26. The rapidly rechargeable battery of claim 1further comprising a battery vessel, wherein the battery vessel issubstantially gas tight.
 27. The rapidly rechargeable battery of claim 1wherein the battery can be charged with high current to reduce chargingtime without irreversible damage.
 28. The rapidly rechargeable batteryof claim 1 wherein the battery can be deeply discharged at high or lowcurrent without irreversible damage.
 29. The rapidly rechargeablebattery of claim 1 wherein the battery can be kept in dry condition fora long period of time.
 30. The rapidly rechargeable battery of claim 1wherein the battery can be kept in charged condition for a long periodof time.
 31. The rapidly rechargeable battery of claim 1 wherein thebattery can be kept in discharged condition for a long period of time.32. A rapidly rechargeable battery utilizing chemical energy of gasescomprising: a gas-tight vessel; an electrolyte contained in thegas-tight vessel; a plurality of gas adsorbing electrodes having aspecific surface area of at least 500 m²/g, immersed in the electrolyte,wherein, during charging, gases are adsorbed on the plurality ofelectrodes; a plurality of electrically conductive components, whereineach electrically conductive component is electrically connected to anelectrode to enable redox reactions at the electrodes; and apermselective membrane disposed around the electrodes that issubstantially impermeable to the gases formed at the plurality ofelectrodes.
 33. The rapidly rechargeable battery of claim 30 furthercomprising separate electrode compartments wherein each electrodecompartment can be filled with a different electrolyte.
 34. A methodcomprising: inserting a plurality of gas adsorbing electrodes into agas-tight vessel, the gas adsorbing electrodes having a specific surfacearea greater than 500 m²/g; disposing around the electrodes apermselective membrane; introducing an electrolyte into the gas-tightvessel, wherein, during charging, gases are adsorbed on the plurality ofelectrodes; and sealing the gas-tight vessel.
 35. A rapidly rechargeablebattery comprising; a plurality of battery cells utilizing chemicalenergy of gases, the battery cells comprising an electrolyte and aplurality of gas adsorbing, high surface area electrodes immersed in theelectrolyte, wherein the battery cells are electrically connected; and aplurality of battery terminals electrically connected to the pluralityof battery cells.
 36. The rapidly rechargeable battery of claim 33wherein the plurality of battery cells are electrically connected inseries.
 37. The rapidly rechargeable battery of claim 33 wherein theplurality of battery cells are electrically connected in parallel. 38.The rapidly rechargeable battery of claim 33 wherein the plurality ofbattery cells are electrically connected in a combination of series andparallel.
 39. A rapidly rechargeable battery utilizing chemical energyof gases comprising: an electrolyte; and a plurality of gas adsorbingelectrodes immersed in the electrolyte wherein each electrode adsorbs atleast 50 cm³/g of a working gas during charging.